1. Field of the Invention
The present invention relates to a horizontal electric field liquid crystal display device which is capable of a clear display even outdoors.
2. Description of the Related Art
Liquid crystal driving methods for liquid crystal display devices include a vertical electric field method in which voltage is applied perpendicular to a substrate, and a horizontal electric field method in which voltage is applied parallel to a substrate. There are advantages and drawbacks to both the vertical electric field method and the horizontal electric field method. For example, compared to the vertical electric field method, which is typified by the TN (Twisted Nematic) method, the horizontal electric field method has qualities such as a wide viewing angle, high contrast, and a high gradation display. The horizontal electric field method is used for monitors and televisions. Each of these kinds of liquid crystal display devices coexists in the field of liquid crystal, and product development is being carried out on them. Further, development is being carried out of liquid crystal materials for use with the horizontal electric field method and of liquid crystal materials for use with the vertical electric field method. The materials have different characteristics depending on the direction that voltage is applied in.
Further, methods for horizontal electric field liquid crystal display devices include an IPS (In-Plane Switching) method and an FFS (Fringe Field Switching) method. Conventional FFS liquid crystal display devices include a device in which one pixel is equipped with a transmissive region and a reflective region (Reference 1: Japanese Published Patent Application No. 2005-107489).
Conventional horizontal electric field liquid crystal display devices are often used for computer monitors, but have not been used for portable electronic device monitors for cellular phones and the like. If applied to a portable device, the device may be used under natural light, and a so-called reflective liquid crystal panel is employed. A design in which the area of a reflective electrode is increased in order to achieve high reflectance is used. However, in a case where the horizontal electric field method is used, if a common electrode and a pixel electrode are made into a reflective electrode to increase the area of the reflective electrode, an electric field that is applied to liquid crystal molecules above the reflective electrode weakens, and liquid crystal molecules might malfunction. As a result, not much development of a reflective-type horizontal electric field liquid crystal display device has been carried out.